In apparatus for generating useful power by reheating gas turbine exhaust gases, with or without a combined steam cycle, conditions of temperature and pressure producing relatively high cycle efficiencies typically involve sufficiently high temperatures and high pressures to necessitate special cooling of gas turbine components. Conventionally, blade cooling is accomplished with air to extract heat from the blade surface.
The physical properties of air limit its effectiveness as a coolant medium, and impose an upper limit to the temperature attainable in a gas turbine. Moreover, air must be sparingly and very carefully used due to its dearness and its effect on cycle degradation both with respect to power and efficiency. At all cycle pressure ratios, and particularly the higher cycle pressure ratios encountered in apparatus involving reheating gas turbine exhaust gases, very little pressure to be available in the small pressure drops allow only region between the compressor discharge and the nozzles and blades for air cooling.
Other approaches to gas turbine component cooling being studied, researched and developed include transpiration air cooling, water cooling and alternative materials of construction capable of withstanding the conditions encountered.
Many additional problems incident to prior approaches to component cooling include corrosion of the metal surfaces at high temperatures, low-cycle metal fatigue, radiant heat absorption, and first-stage nozzle and blade surface fouling during start-up and operation. The following references are cited as background for the present invention and disclose the proposed combined reheat gas turbine and steam turbine cycle which is the basis of the parent application, U.S. Ser. No. 954,838.
(1) Rice, I. G., "The Combined Reheat Gas Turbine/Steam Turbine Cycle", Part I--"A Critical Analysis of the Combined Reheat Gas Turbine/Steam Turbine Cycle", ASME Paper No. 79-GT-7, ASME Journal of Engineering for Power, 1979
(2) Rice, I. G., "The Combined Reheat Gas Turbine/Steam Turbine Cycle", Part II--"The LM 5000 Gas Generator Applied to the Combined Reheat Gas Turbine/Steam Turbine Cycle", ASME Paper No. 79-GT-8, ASME Journal of Engineering for Power, 1979
The above references describe essentially the invention disclosed in the parent application for patent of which this is a continuation-in-part. Other material pertinent to the present invention include published studies of the effects of steam injection on the performance of gas turbine power cycles for combined cycles, where steam is evaluated as a form of injection to augment power and to control nitrogen oxide emissions. However, no studies have been made with respect to the combined reheat gas turbine and steam turbine cycle without intercooling as the combined cycle of the present invention and no evaluation of steam as a coolant is presented as a way to optimize the combined gas turbine and steam turbine cycle, nor is the apparatus disclosed herein described.